This invention relates generally to multisection telescoping rods and more particularly, to telescoping measuring rods (e.g., leveling rods).
As sections of a telescoping rod reach their full extended position with respect to each other, the sections should lock to hold the sections in a fixed position of extension, allowing neither further extension nor retraction of the sections relative to one other. However, the locking mechanism must also be easily releasable for retraction of the inner section. Reference may be made to U.S. Pat. Nos. 4,385,849 and 4,318,228 describing extensible and retractable rods generally in the field of this invention.
U.S. Pat. No. 4,318,228 shows a leveling pole which has multiple telescoping sections with a locking mechanism for holding adjacent sections in a fixed position of extension with respect to each other. The locking mechanism comprises a locking button mounted on a coil compression spring in an inner section. The spring biases the button outwardly so that the button will move in a substantially straight line into an opening in an outer section immediately adjacent the inner section, to lock the sections. The locking button has an outwardly facing surface sloping continuously inwardly from top to bottom of the button. As the locking button begins to register with the opening in the outermost section, the upper portion of the locking button begins to project into the opening because of the inward slope of the locking button's outwardly facing surface. When the lower edge of the locking button registers with the opening, the locking button springs into its full outward position so that a lower surface of the locking button is engageable with the lower edge of the opening and the upper surface of the locking button is engageable with the upper edge of the opening to hold the inner and outer sections in an extended position.
Because the outwardly facing surface of the locking button shown in U.S. Pat. No. 4,318,228 slopes continuously inwardly from top to bottom when the button is in its locking position, the outer edge of its lower surface is positioned inwardly of the outer edge of its upper surface. Therefore, to be positioned for engagement with the lower edge of the opening, the locking button must project through the opening in the outer section far enough to bring its lower surface over the lower edge of the opening. Accordingly, the outer edge of the upper surface must project a relatively substantial distance beyond the outer surface of the outer section. This arrangement works satisfactorily so long as the outer section has been extended from a next outer section, immediately adjacent the outer section, so that the opening in the section is clear of the inner surface of the next outer section. Absent this clearance, the locking button could not project through the opening far enough before engaging the inner surface of the next outer section to allow its lower surface to be positioned for engagement with the lower edge of the opening in the outer section. Thus, there would be nothing to hold the inner section from retracting relative to the outer section.
Certain leveling rods operate by extension of their innermost sections first, with the level being read at the top of the outermost section of the rod. In this design, adjacent inner and outer sections must be able to lock while the opening in the outer section is positioned inside of the next outer section. With respect to this type of rod, use of the locking button shown in U.S. Pat. No. 4,318,228 would be unsatisfactory because the locking button could not project through the opening far enough to allow its lower surface to be positioned for engagement with the lower edge of the opening. Thus, there would be nothing to hold the inner section from retracting. Additional space could be provided between the outer section and succeeding outer section, such as by increasing the diameter of the next outer section. However, because a leveling rod is typically made up of a number of interlocking sections, the outermost section would have to be of relatively large diameter, making the rod more difficult to manipulate.
In another aspect, the outer surfaces of each section of a leveling rod have indicia, usually in feet, on an outer surface of the section. These indicia are typically painted on the sections, and are gradually worn off by the frictional engagement of adjacent sections as they are extended and retracted with respect to each other. This necessitates periodic disassembly of the leveling rod and repainting of the indicia, which is time consuming and causes increased down time and maintenance cost.